The present invention relates to an adaptive array antenna system, in particular, relates to such a system which can automatically calibrate amplitude and phase of each array antenna elements during communication in the system itself used in communication system such as TDD (Time Division Duplex) which carries out transmission and reception on time division basis.
Lately, due to rapid expansion of mobile communication such as a portable telephone set and/or PHS (Personal Handyphone System), it becomes essential to have subscribers as many as possible in limited frequency band. Therefore, a multi-channel access system in which a specific channel is shared by a plurality of subscribers is now widely used in mobile communication system. The typical multi-channel access system used in the current mobile communication system such as cellular system and/or PHS, is Time Division Multiple Access (TDMA) system. Further, in a micro-cell system which is excellent in frequency usage efficiency, a Time Division Duplex (TDD) system which shares transmission and reception on the same frequency on time division basis is used.
On the other hand, it is essential to get rid of interference from adjacent cells in order to have high frequency usage efficiency in radio channels. The conventional technique to improve frequency usage efficiency is the use of an adaptive array antenna system. This is described in Monzingo et al, xe2x80x9cIntroduction to Adaptive Arrayxe2x80x9d, John willy and Sons, New York, 1980. An adaptive array antenna system has an array of antenna elements each having weighted input signals for amplitude and phase so that the antenna system has null directivity on a radiation pattern in the direction of an interference wave to get rid of affection of an interference wave.
FIG. 13 shows a conventional configuration when an adaptive array antenna is used in a TDD system. When an adaptive array antenna is used in a TDD system, it is possible to use a radiation pattern of an antenna in a receive side as a radiation pattern in a transmit side as it is since transmit frequency is the same as receive frequency. Therefore, an adaptive array antenna is suitable to a TDD system considering transmit characteristics.
In FIG. 13, numerals 13-1-1 through 13-1-N show N (N is an integer larger than 2) number of element antennas, each coupled with transmitters 13-3-1 through 13-3-N or receivers 13-4-1 through 13-4-N through transmit/receive switches 13-2-1 through 13-2-N.
A receive signal is applied to a receiver through an antenna element, and a transmit/receive switch. An output of the receiver is applied to a radiation pattern control calculation circuit 13-7 (or direction control calculation circuit) which calculates amplitude and phase of each channel. A weight multiplier circuit 13-6 multiplies said amplitude and said phase to a signal to be transmitted, and the product is applied to antenna elements through transmitters and transmit/receive switches. The amplitude and the phase of the antenna elements are controlled by the weight multiplier circuit so that a desired shape of an antenna beam is obtained.
Accordingly, when the radiation pattern control calculation circuit provides the amplitude and the phase of each channels, and the weight multiplier circuit provides the product of said amplitude and the phase, and the transmit signal, the transmit radiation pattern is essentially the same as the receive radiation pattern.
However, although an amplitude and a phase of an antenna element should be ideally the same as those in all the antenna elements, they are actually different from one another because of an error of a high frequency circuit including a power amplifier, a connection cable, and/or temperature variation where an apparatus is mounted. The error degrades null and side lobe, so that interference suppression characteristics of an adaptive array antenna are degraded. This is described in J. Litva et al, xe2x80x9cDigital Beamforming in Wireless Communicationsxe2x80x9d, Artech House Publishers, 1996.
FIG. 11 shows an example of the degradation. FIG. 11 shows three elements circularly arranged array antenna. FIG. 11(a) shows the case of ideal amplitude/phase relations, and FIG. 11(b) shows the depth of null in the radiation pattern because of an error of amplitude and/or phase of each antenna element. When it is ideal, a pattern having a null in 180xc2x0 direction is obtained as shown in FIG. 11(a). However, when an error exists in amplitude and/or phase in each antenna element, a radiation pattern is considerably degraded as shown in FIG. 11(b). Accordingly, when transmit radiation pattern should coincide with receive radiation pattern of an adaptive array antenna in TDD system, amplitude and phase in each branches in an array antenna should be adjusted.
Conventionally, when amplitude and phase of an array antenna is adjusted, a signal from far field, or a signal transmitted by an array antenna in far field is received, and phase of each branches is sequentially rotated. This is called an element field vector rotation method, and is described in xe2x80x9cA Method for Measuring Amplitude/Phase of Antenna Element in Phased Array Antennaxe2x80x9d, by Mano, and Kataki, in Technical Journal (B), published by Institute of Electronics, Information and Communication in Japan, vol. J-65-B, No.5, pages 555-560.
However, when base stations are not positioned regularly in a micro-cell mobile communication system, but are positioned considering elimination of out-of-service area in a service area, and/or traffic, it is impossible to use above method in each base stations.
Further, when we try that a terminal station transmits a signal for adjustment purpose, said signal must be transmitted during actual communication, and therefore, transmission efficiency of a communication frame is decreased.
Accordingly, in an environment of mobile communication system, it is desired that amplitude and phase of each branch is adjusted by using an actual communication apparatus itself.
A prior proposal to adjust amplitude and phase of each branch by using an actual communication apparatus itself, is that an apparatus has a reference signal for adjustment purpose, and an array antenna is adjusted by using said reference signal. This is described in H. Steyscal et al, xe2x80x9cDigital Beamforming for Readersxe2x80x9d, Microwave Journal, vol.32, no.1, pp121-136. The configuration of the adjustment circuit in that article is shown in FIG. 12.
In FIG. 12, an array antenna is adjusted as follows.
(1) A reference signal generator 12-11 sends a signal which is common to all the branches to a receiver 12-3 through a separator 12-14a. An adjusted value for each receiver is determined based upon a value received in each receiver and a reference value which is a received value by a specific receiver.
(2) A transmitter 12-4 sends a signal to a receiver through a switch 12-13, and an attenuator 12-12. The adjusted value is obtained by an output of each receiver, and a reference value of a reference receiver which is defined in said process (1).
(3) The transmit adjustment value is obtained by the difference of said process (1) and said process (2).
Accordingly, FIG. 12 can adjust amplitude and phase of each branch of an array antenna by using only a communication apparatus.
However, FIG. 12 carries out the adjustment of a transmitter and a receiver independently, and therefore has the disadvantage that an adjustment can not be carried out during actual communication in TDD system which carries out transmission and reception on time division multiplex system. Therefore, it can not follow the change of environment such as temperature variation during communication and/or change of location of base stations.
An object of the present invention is to provide an adaptive array antenna which can be adjusted during actual communication by using only a communication apparatus itself. The present invention does not use an external signal for adjustment of amplitude and phase of each branch, and therefore, no degradation of transmission efficiency occurs.
The feature of the invention to attain the above objects resides in an adaptive array antenna system comprising; N (N= greater than 2, N is an integer) number of antenna elements (1-1-1 through 1-1-N); N number of transmitters (1-3-1 through 1-3-N); N number of receivers (1-4-1 through 1-4-N); a directivity calculation circuit (1-7) for controlling radiation pattern of said adaptive antenna system by weighting amplitude and phase of signals applied to a respective receiver related to each antenna element, and combining weighted signals; said adaptive array antenna being used in Time Division Duplex communication system; each transmitter being coupled with a related antenna element during transmit time slot in communication, and having means (1-5-1 through 1-5-N) for sending a part of transmit signal to at least one receiver; amplitude/phase calibration calculation circuit (1-6) receiving outputs of at least two receivers which receive a signal from a transmitter during transmit time slot, and providing amplitude/phase calibration value of a branch related to said transmitter and said receivers by ratio of outputs of said at least two receivers.
In an embodiment of the present invention, an adaptive array antenna system according to the present invention comprises; N (N= greater than 2, N is an integer) number of antenna elements (2-1-1 through 2-1-N); N number of transmitters (2-3-1 through 2-3-N); N number of receivers (2-4-1 through 2-4-N); N number of first switches (2-2-1 through 2-2-N) provided for each antenna element for selectively coupling a respective antenna element either to a respective transmitter or to a respective receiver; a radiation pattern control calculation circuit (2-10) for controlling radiation pattern of said array antenna by weighting signals applied to each receivers with amplitude and phase, and combining weighted signals; a weight multiplier circuit (2-11) for multiplying transmit signal and amplitude and phase obtained in said radiation pattern control calculation circuit; N number of separators (2-5-1 through 2-5-N) provided for each transmitters for coupling an output of a respective transmitter to a respective antenna element and separating a part of transmit signal; a second switch (2-6) for coupling a signal separated by the first separator (2-5-1) with one of second through N""th receivers (2-4-2 through 2-4-N); a third switch (2-7) for coupling signals separated by second through N""th separators (2-5-2 through 2-5-N) with the first receiver (2-4-1); fourth switches (2-8-1 through 2-8-N) for coupling an input of each receiver (2-4-i) with either a signal of a respective antenna element (2-1-i) through a respective first switch (2-2-i), or a signal from said second switch (2-6) or said third switch (2-7); an amplitude/phase calibration value calculation circuit (2-9) for providing amplitude/phase calibration value of each antenna element by using an amplitude value and a phase value obtained in each receivers.
Preferably, said amplitude/phase calibration value calculation circuit (2-9) provides calibration value of i""th antenna element by; separating a signal from first transmitter (2-3-1); coupling the separated signal with i""th (2= less than i= less than N, i is an integer) fourth switch (2-8-i) through said second switch (2-6); obtaining a value (1) at an output of said i""th receiver (2-4-i) which receives said separated signal through i""th fourth switch (2-8-i); separating a signal from i""th transmitter (2-3-i); coupling the separated signal with first fourth switch (2-8-1) through said third switch (2-7); obtaining a value (2) at an output of first receiver (2-4-1) which receives said separated signal from i""th transmitter (2-4-i); and providing ratio of (said value (1))/(said value (2)) as calibration value of i""th branch.
According to another embodiment of the present invention, an adaptive array antenna system comprises; N (N= greater than 2, N is an integer) number of antenna elements (4-1-1 through 4-1-N); N number of transmitters (4-3-1 through 4-3-N); N number of receivers (4-4-1 through 4-4-N); first switches (4-2-1 through 4-2-N) provided for each antenna element for switching an antenna element (4-1-i) either to a respective transmitter (4-3-i) or to a respective receiver (4-4-i); a radiation pattern control calculation circuit (4-10) for controlling radiation pattern of said adaptive array antenna system by weighting amplitude and phase of a signal applied to each receivers and combining weighted values; a weight multiplier circuit (4-11) for multiplying transmit signal, and amplitude and phase obtained in said radiation pattern control calculation circuit; N number of separators (4-5-1 through 4-5-N) for separating an output of each transmitter into two signals; (Nxe2x88x922) number of second switches (4-6-2 through 4-6-(Nxe2x88x921)) for connecting an input of k""th receiver (4-4-k) either to (kxe2x88x921)""th separator (4-5-k) (2 less than =k less than =Nxe2x88x921, k is an integer) or to (k+1)""th separator (4-5-(k+1)); (Nxe2x88x922) number of third switches (4-7-2 through 4-7-(Nxe2x88x921)) for connecting k""th separator (4-5-k) either to an input of (k-xe2x88x921)""th receiver (4-4-(kxe2x88x921)) or an input of (k+1)""th receiver (4-4-(k+1)); fourth switches (4-8-1 through 4-8-N) for connecting an input of a respective receiver (4-4-i) either to a respective antenna element (4-1-i) through one (4-2-i) of said first switches, or to a signal from said second switch (4-6-i) or said third switch (4-7-i); an amplitude/phase calibration value calculation circuit (4-9) for providing amplitude/phase calibration value of each antenna element by using an amplitude value and a phase value obtained in each of said receivers.
Preferably, said amplitude/phase calibration value calculation circuit (4-9) calculates;
C(i)=A(i)/B(i), (1 less than =i less than =Nxe2x88x921, i is an integer) and assigns amplitude/phase calibration value of (i+1)""th branch so that;
C(i) when i=1
D(i)=C(ixe2x88x921)C(i) when ixe2x89xa01
where A(i) is an output of (i+1)""th receiver (4-4-(i+1)) which receives an output of i""th transmitter (4-3-i) through i""th separator (4-5-i), said second switch (4-6-(i+1)), and (i+1)""th fourth switch (4-8-(i+1)), and B(i) is an output of i""th receiver (4-4-i) which receives an output of (i+1)""th transmitter (4-3-(i+1)) through (i+1)""th separator (4-5-(i+1)), said third switch (4-7-i), and i""th fourth switch (4-8-i).
According to still another embodiment of the present invention, an adaptive array antenna system comprises; N (N= greater than 2, N is an integer) number of antenna elements (6-1-1 through 6-6-N); N number of transmitters (6-3-1 through 6-3-N); N number of receivers (6-4-1 through 6-4-N); first switches (6-2-1 through 6-2-N) for switching each antenna element (6-1-i) either to a respective transmitter (6-3-i) or to a respective receiver (6-4-i); a radiation pattern control calculation circuit (6-10) for controlling radiation pattern of said adaptive array antenna system by weighting amplitude and phase of a signal applied to each receivers and combining weighted values; a weight multiplier circuit (6-11) for multiplying transmit signal, and amplitude and phase obtained in said radiation pattern control calculation circuit; N number of separators (6-5-1 through 6-5-N) provided for each transmitters for separating an output signal of each transmitter; a second switch (6-6) for connecting a signal from a first separator (6-5-1) to one of first through N""th receivers (6-4-1 through 6-4-N); a third switch (6-7) for connecting an input of a first receiver (6-4-1) to one of first through N""th separators (6-5-1 through 6-5-N); N number of fourth switches (6-8-1 through 6-8-N) for connecting an input of a respective receiver (6-8-i) either to a first antenna element (6-1-1) through a first switch (6-2-1), or to a signal from a second switch (6-6) or a third switch (6-7); an amplitude/phase calibration value calculation circuit (6-9) for providing amplitude/phase calibration value of each antenna element by using an amplitude value and a phase value obtained in each receivers.
Preferably, said amplitude/phase calibration value calculation circuit (6-9) provides calibration value of i""th antenna element by; separating a signal from a first transmitter (6-3-1) by using a first separator (6-5-1); coupling the separated signal with i""th (1 less than =i less than =N, i is an integer) fourth switch (6-8-i) through said second switch (6-6); obtaining a value (1) at an output of i""th receiver (6-4-i) which receives said separated signal through i""th fourth switch (6-8-i); separating a signal from i""th transmitter (6-3-i) by using an i""th separator (6-5-i); coupling the separated signal with first fourth switch (6-8-1) through said third switch (6-7); obtaining a value (2) at an output of a first receiver (6-4-1) which receives said separated signal from i""th transmitter (6-3-1) through said first fourth switch (6-8-1); and providing ratio of (said value (1))/(said value (2)) as calibration value of i""th antenna element.
According to still another embodiment of the present invention, an adaptive array antenna system comprises; N (N greater than =2, N is an integer) number of antenna elements (9-1-1 through 9-1-N); N number of transmitters (9-3-1 through 9-3-N); N number of receivers (9-4-1 through 9-4-N); a first switch (9-2-1 through 9-2-N) provided for each antenna elements for switching an antenna element either to a respective transmitter or to a respective receiver; a radiation pattern control calculation circuit (9-10) for controlling radiation pattern of said adaptive array antenna system by weighting amplitude and phase of a signal applied to each receivers and combining weighted values; a weight multiplier circuit (9-11) for multiplying transmit signal, and amplitude and phase obtained in said radiation pattern control calculation circuit; N number of separators (9-5-1 through 9-5-N) provided for each transmitters for separating a signal from a respective transmitter; a second switch (9-6) for connecting a signal of a first separator (9-5-1) to one of first through N""th receivers (9-4-1 through 9-4-N); a third switch (9-7-2 through 9-7-N) for connecting an input of k""th receiver either from a first separator (9-5-1) or from k""th (2 less than =k less than =N, k is an integer) separator; N number of fourth switches (9-8-1 through 9-8-N) for connecting an input of a respective receiver to a signal either from a respective antenna element through a respective first switch, or from said second switch or said third switch; an amplitude/phase calibration value calculation circuit (9-9) for providing amplitude/phase calibration value of each antenna element by using an amplitude value and a phase value obtained in each receivers.
Preferably, said amplitude/phase calibration value calculation circuit calculates;
C(i)=A(i)/A(1)
D(i)=B(k=i)/A(i)
and assigns C(i)/D(i) as an amplitude/phase calibration value of i""th antenna element,
wherein;
A(i) is an output of i""th receiver (9-4-i) which receives an output of a first transmitter (9-3-1) through a first separator (9-5-1), a second switch (9-6), and i""th fourth switch (9-8-i), and B(k), (2 less than =k less than =N, k is an integer), is an output of k""th receiver (9-4-k) which receives an output of k""th transmitter through k""th separator (9-5-k), a third switch (9-7-2) and k""th fourth switch (9-8-k).
In a prior art, a transmit section in a transceiver is calibrated independently from a receive section in the transceiver in order to coincide a transmit pattern of an antenna with a receive pattern of the antenna. Therefore, both a calibration device for a transmit section and a calibration device for a receive section are requested.
An adaptive array antenna may in general reduce interference in a receive mode by properly forming a directivity of an antenna even when amplitude and/or phase error among branches exists. A transmission is enough by using an antenna pattern which is the optimum in a receive mode, and therefore, both the transmit section and the receive section may be calibrated during transmission period in a TDD system in which transmission and reception are carried out alternately.
According to the present invention, a plurality of loops which feed back a transmit signal to a receiver are provided so that a transmit signal is fed back not only to a receiver of the same branch of the transmitter, but also to receivers of other branches. In other words, a transmit signal is not only fed back to a receiver of the branch of the transmitter as is the case of a prior art, but also a transmit signal is fed back to other branches, so that calibration of both the transmit section and the receive section are obtained.
In an embodiment in FIGS. 2 and 3, a single branch is assigned as a reference branch, and a transmit signal of the reference branch is applied to the receivers of other branches, so that values of a transmitter and a receiver are calibrated during communication, and an amplitude/phase calibration value calculation circuit is calibrated.
In an embodiment in FIGS. 4 and 5, a number of contacts of switches for feed back of a reference signal to receivers are reduced. In this embodiment, a calibration value is calculated between two adjacent branches, initially, a first branch and a second branch. Then, a pair of two branches are shifted in sequence, so that the calibration values of all the branches are obtained. The calibration of an amplitude/phase calibration value calculation circuit is shown in this embodiment.
In an embodiment of FIGS. 6, 7 and 8, not only calibration values of a transmit section and a receive section are obtained during communication, but also, a calibration value of a transmit section is obtained separately from a calibration value of a receive section. The calibration of an amplitude/phase calibration value calculation circuit is also shown in this embodiment.
In an embodiment of FIGS. 9 and 10, not only, calibration values of a transmit section and a receive section are obtained during communication, but also, a calibration value of a transmit section is obtained separately from a calibration value of a receive section. This embodiment has further a feature that a wiring in a calibration circuit is short since a transmit signal except for a reference branch is only fed back to a receiver of the same branch as that of the transmit signal. The calibration of an amplitude/phase calibration value calculation circuit is also shown in this embodiment.